Living history: Tracking lake sturgeon

Lake sturgeon have been around since the age of the dinosaurs. They did the one thing dinosaurs couldn’t do: They adapted, and they survived.

But, leave it to mankind to push one of nature’s oldest creatures to the verge of extinction. Thanks largely to the loss of habitat and pollution, lake sturgeon are currently classified as an endangered species.

In order to monitor the health and the sustainability of this ancient species, the Michigan Department of Natural Resources conducts annual lake sturgeon assessment counts in the North Channel of the St. Clair River. Since 1997, the DNR spends three weeks, from late May to mid-June laying out eight set-lines of 25 baited hooks along the bottom of the channel to catch the sturgeon. Sturgeon remain on the hook for a maximum of 24 hours before they are pulled up.

They are then weighed, measured and have a microchip embedded behind their head to monitor their movements. A numbered tag is clipped to their dorsal fin, which fishermen can report to the DNR, and, if the fish is small and younger, a piece of a pectoral fin is removed for further examination. The pectoral fin sample is 2-3 inches long by about a half an inch thick and grows back in one to two years. The fin sample is used to determine the age of individual fish. It is sectioned off and observed under a microscope. The analysis is similar to looking at rings on a tree stump.

The Algonac area of the St. Clair River has the largest area of free-range sturgeon population in the Great Lakes basin. In other areas, such as Black Lake, located in the northeast portion of the Lower Peninsula, the sturgeon are land locked and unable to move freely through the basin.

Sturgeons are most vulnerable in the spring when they spawn in shallow rivers and tributaries and can literally be hand-plucked out of the water and stripped of their caviar, although the DNR says increased public knowledge over the plight of the sturgeon has reduced those incidents.

The young sturgeon are then subject to predators for about six months, or the fall season, when they swim away from their nesting grounds. Adult sturgeon can grow to 6-8 feet long, weigh 200 pounds and live for 100 years. After travelling for thousands of miles, they return to the exact location they were born every 3-7 years to spawn. Female sturgeon spawn every three to seven years, while males spawn every three to five years.

Lake sturgeon are also a valuable barometer on the health of a watershed, in this case the Great Lakes basin, because they are what is called a “keystone” species. They are given that title because they are the largest animal in the Great Lakes, yet they are bottom feeders and feed on the smallest organisms in the water column, such as quagga mussels and zebra mussels, snails, mayfly nymphs other small aquatic invertebrates found on the bottom. They will also eat dead fish, which explains why the DNR has success catching sturgeon on hooks baited with gobies. So they are omnivores, opportunists who aren’t afraid to expand their menu. But the fact that their primary diet is bottom-of-the-food-chain invertebrates yet they grow so large and live so long makes them unique.

Thus, the existence of a healthy keystone species like the lake sturgeon in a particular watershed means the entire watershed is healthy.

While the DNR has been conducting its annual set line sturgeon survey since 1997, 2013 marks the second year of a 3-year study in which the battery-powered microchip transmitters are being inserted in sturgeon behind the head. The transmitters have a 10-year battery life, and receivers are strategically placed around the movement patterns of the fish across the Great Lakes basin. The transmitters have about a one kilometer range. The receivers are then picked up and the data on them is downloaded.

“Across the state of Michigan, sturgeon are at a remnant level of the population that was historically present here. Lake St. Clair is one of the few remaining strong and self-sustaining populations,” said Mike Thomas, a fisheries research biologist for the Lake St. Clair Fisheries Research Station. “It’s important for us to know whether it’s increasing in size or stable or decreasing. This monitoring program is the only way to tell that and to make sure they are healthy into the future.

“With the survey and the mark and recapture work that we are doing, we estimate the total population is around 15,000 (in the St. Clair River watershed), both young and adults. We see them moving around in south Lake Huron, Lake Erie, and they spend some time here. The big fish move around. The little fish tend to stick in the North Channel.”

Research has shown that lake sturgeon migration is quite complex. Rather than moving north and south in strict patterns the way birds migrate, sturgeon move in and out of the St. Clair River during spawning times in irregular patterns and others stay in the river. While they all will return to the place where they were born to spawn, there is no set pattern to what they do in the meantime. But the fact that they spend so much time in the river is a positive sign regarding the overall health of the river.

“It’s definitely a sign from an ecological standpoint that if you have a good, healthy lake sturgeon population, it’s a positive sign that the ecological system is in good shape,” Thomas said. “And it also helps to keep the eco system in good shape to have a robust sturgeon population because of the energy that is represented by those fish is in a stable form and doesn’t lend itself to big fluctuations that you would have with energy tied up in a really short-lived fish like an alewife or some other invasive species that would be prone to quick oscillations in abundance.”

This year, the sturgeon count collected 100 fish during the 3-week survey, an average collection. About 30 percent of the fish are specimens previously caught and examined. On June 20, the second-to-last day of the survey, the DNR crew caught one sturgeon for the fourth time. The 10-year-old was first caught in 2007, again in 2010, 2011 and this year. Of the 10 fish caught that day, the two largest were nearly five feet long, close to 60 pounds, and had more than two feet of girth. Fish that size are estimated to be between 25 and 50 years of age and most likely female.

Despite modern obstacles facing wildlife today, the lake sturgeon has been able to adapt and survive over thousands of years. And while endangered, Thomas said he’s very confident the population that spends at least part of its life in the St. Clair River is at the very least stable.

“They’ve evolved to fit the habitat. In areas where there is more human activity, like dams blocking off their spawning locations and pollution removing the oxygen from the bottom of the river and their eggs wouldn’t survive like has happened in other parts of the Great Lakes, they haven’t done well,” he said. “But they’ve been able to do quite well here.”